Automatic Speech Recognition (ASR) systems have begun to gain wide acceptance in a variety of applications. U.S. Pat. No. 4,827,500 issued to Binkerd et al. on May 2, 1989 describes a technique for Automatic Speech Recognition to Select Among Call Destinations in which a caller interacts with a voice response unit having an ASR capability. Such systems either request a verbal input or present the user with a menu of choices, then wait for a verbal response, interpret the response using ASR, and carry out the requested action, all without human intervention.
An important issue in designing the user interface to a system using ASR concerns the issue of handling the potential for recognition errors, since it is recognized that whenever an ASR system interprets an utterance, there is some residual uncertainty as to the correspondence between the utterance and the interpretation. This problem is especially important for input of digit strings, such as in a system in which telephone numbers or credit card numbers are spoken by the caller, because it is not uncommon to have an overall accuracy rate of only 85 to 90 percent for a digit string (and, in some cases, even for a segment of a digit string). To deal with potential errors, systems today use some type of explicit verification for all transactions where the error rate causes concern in order to avoid the possibility of processing an incorrect digit string. For example, following input of each connected digit string, the ASR system may "read back" the best digit string candidate, and require an affirmative or negative response from the individual using the system. An example would be: "Please say `yes` if your credit card number is XXX-YYYY, and please say `no` otherwise". While this type of explicit verification is often necessary and useful, it is cumbersome, time consuming and annoying, especially for frequent users of the ASR system, or users for whom the ASR system has a high degree of confidence. Other systems have requested a user to re-input a speech request if a previous request could not be recognized. However, when recognition does occur, a static verification process is employed.